Lamp flashing circuits



July 24, 1962 c, KNUDSON 7 3,046,448

LAMP FLASHING CIRCUITS I Filed June 8, 1959 OFF r/ME INVENTOR. CZA/QEA/CE 8. (Ml/030M ONE CYCLE -1 d i J 3,046,448 LAMP FLASHING CIRCUITS Clarence B. Knudsen, Inglewood, Calif, assignor to Hughey & Phillips, Inc, Burbank, Calif., a corporation of California Filed June 8, 1959, Ser. No. 818,777 8 Claims. (Cl. 315-419) This invention relates to improved flashing circuits for obstruction marking and warning lights such as are utilized on radio towers and on other obstructions of any sort.

In the past warning or marker lights used on radio towers and other obstructions have commonly been made to flash, so as to be more effective in arresting the attention of any person approaching the obstruction, through the mechanism of a mechanical circuit breaker. More recently electronic switches such as power transistors have been utilized to switch between on and off conditions. However, in general, these transistorized circuits have been utilized to flash relatively low voltage lamps, such as 6 volt lamps, and the problem of flashing high voltage lamps, such as 110 volt lamps, has not been successfully accomplished with transistorized circuits. Further, transistorized circuits conventionally operate from low voltage battery power sources and power consumption, which affects battery life, becomes a significant factor to consider. It is highly desirable, for maximum effectiveness of the warning or marking equipment, that a high voltage lamp be used and that the system operate from a low voltage battery with a minimum power consumption from the battery for a desired amount of light intensity.

Therefore, it is an object of this invention to provide an improved transistorized circuit which will permit the operation of a high voltage warning lamp from a low voltage battery circuit.

It is a further object of this invention to provide an improved transistorized lamp flashing circuit which will cause the lamp to exhibit greater attention-arresting characteristics as a warning device While requiring less average power from the associated battery power source, thus assuring maximum battery life.

According to the present invention, a transistorized power oscillator operating at a frequency in the range, for example, of 1,000 cycles per second, is self-quenched, and is keyed by a low frequency transistorized oscillator having desired on and off characteristics and drives pulses of current through a voltage step-up transformer to a high voltage lamp during the power oscillator on time. Because pulses are being used to operate the warning lamp rather than a steady current the average power consumed by the lamp is reduced and the life of the low voltage battery supplying power for the system is increased. At the same time the self-quenching action produces a perceptible and attention-arresting flicker is the light output from the lamp during on periods.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The'present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which,

FIGURE 1 is a circuit diagram of a first embodiment of this invention.

FIGURE 2 is a circuit diagram showing an alternative form of the circuit of FIGURE 1.

FIGURE 3 is a graphical representation of the light output obtained from the circuit of FIGURE 2.

In FIGURE 1, which shows the electrical pulse generator of this device and which comprises a blocking oscillator operating in the sub-audible range and a power oscil: lator operating in the audio range, transistor 10 has its emitter 11 connected to secondary 12 of transformer 13. The remaining terminal of secondary 12 of transformer 13 is connected to terminal 14 which is adapted for connection to the negative terminal of a source of direct current, such as a battery. Condenser 15 shunts secondary 12 of transformer 13. Base 16 of transistor 10 is connected through a variable resistor 17 to one terminal of capacitor 18 the other terminal of which is connected to one end of primary winding 19 on transformer 13, the other end of such winding being connected to negative terminal 14. Resistor 20 shunts the series combination of capacitor 18 and primary winding 19.

Collector 21 of transistor 10 is coupled through resistor 22 to one terminal 23 of voltage dividing resistor 24 and to center tab- 25 of winding 26 on output transformer 27. The remaining terminal 28 of resistor 24 is coupled through resistor 29 to the junction 30 formed between one terminal of resistor 20 and one terminal of capacitor 18. Terminal 28 of resistor 24 is connected to emitter 31 of output transistor 32 and to emitter 33 of output transistor 34. Positive operating potential is applied from terminal 35 through switch 36 to terminal 28. Base 37 of output transistor 32 is connected to one end of winding 26 on output transformer 27, the other end of that winding being connected to base 38 of output transistor 34. Collector 39 of transistor 32 is connected to one extremity of a second winding 40 of transformer 27, the other end of such winding 40 being connectedto collector 41 of transistor 34. Secondary winding 42 of output transformer 27 is connected to lamp 43 which may be of the volt incandescent variety or, with the proper magnitude for secondary winding 42, may be a gas filled lamp.

The blocking oscillator circuit of FIGURE 1 operates as follows. With the closing of switch 36 a small forward bias is applied to base 16 of transistor 10 and the current begins to flow through emitter 11 and, consequently,

through winding 12 of transformer 13. This flow of current through winding 12 produces a changing magnetic flux which induces a voltage in winding 19", the direction of the winding 19 being such that this induced voltage from winding 12 adds to the forward bias already applied to junction 30 as a. result of the voltage dividing network comprising resistors 29 and 20. The current in emitter 11 is thus caused to increase and, as a result of' this regenerative process, transistor 10' is driven rapidly to a condition of current saturation at which the current flowing in emitter 11 becomes steady thus causing the flux surrounding winding 12 to become steady thereby removing the induced and aiding voltage in winding 19. The fiux surrounding the windings now starts to decrease and the rate of decrease is determined by the charge on capacitor 15 and the resistance of winding 12. The de-' creasing flux causes a reversalin polarity of the potential appearing across winding 19 which applies reverse bias to base 16 of transistor 10 thereby reducing emitter current 11. Emitter current 11 is further reduced by repeated further reductions of the aiding forward bias at junction 30 and transistor 10 is rapidly cut off. During the portion of the cycle in which emitter current 11 was rising capaci tor 18 acquired a small charge. The total cycle of operaitor 18 by a sufficient marg'n to permit conduction in the base-emitter circuit of transistor 10. The pulse generating cycle just described is then repeated.

Capacitors 15 and 18, and their associated components, thus provide timing circuits that establish the cycling rates of the blocking oscillator in the well-known way.

When transistor is in a non-conducting state base 37 of output transistor 32 and base 38 of output transistor 34 (together forming a p-n-p push-pull power oscillator) are reverse biased from positive terminal 35 through switch 36, resistor 24 and winding 26 of output transformer 27. Thus, under this condition, the output power applied to lamp 43 is at a zero level. However, when transistor 10 conducts, bases 37 and 38 are connected through a low impedance path including resistor 22 and the collector-emitter circuit of transistor 10 to negative terminal 14, thus forward-biasing transistors 32 and 34 and producing a current flow between the emitter and collector of each of those transistors. The relative directions of the two windings 26 and 40 is such that regeneration occurs in the base-collector circuits of the two transistors 32 and 34 and oscillation occurs. These oscillatory currents are transformed by secondary winding 42 to produce a voltage adequate to operate lamp 43.

In FIGURE 2 the configuration of components in the self-quenching, transformer coupled oscillator incorporating transistor 10 is the same as it was in the circuit of FIG- URE 1. The only changes in circuitry between FIG- URES 1 and 2 occur beyond the junction points A, B and C in FIGURES l and 2. In substance transistors 32 and 34 are connected in a grounded emitter configuration in FIGURE 1 and are connected in a grounded collector configuration in FIGURE 2. The grounded collector configuration of FIGURE 2 has the advantage that transistors 32 and 34 need not be insulated from the chassis on which they are mounted and hence more effective heat sinking can be achieved.

Specifically, in FIGURE 2, winding 40 of output transformer 27 is connected between emitter 31 of transistor 32 and emitter 33 if transistor 34 and has a center tap connected through switch 36 to positive terminal 35. Collectors 39 and 41 are connected together and to negative terminal 14. As in FIGURE 1, winding 26 is connected between base 37 of transistor 32 and base 38 of transistor 34. The operation of the circuit of FIGURE 2 is fundamentally the same as that of FIGURE 1 in that output transistors 32 and 34 are normally biased off through a voltage divider network including resistor 24 but when transistor 10 conducts during its operation as a blocking oscillator the reverse bias is essentially removed from transistors 32 and 35 and they are permitted to conduct, which results in oscillations in the output circuit and power transfer at the proper voltage level through secondary 42 to lamp 43.

If the light output from lamp 43 is measured by a photoelectric device coupled to an oscilloscope, or the like, the light output from lamp 43 is seen to be pulsating as shown in FIGURE 3. If it is desired that the pulsed characteristics of the light from lamp 43 correspond to those characteristics exhibited in FIGURE 3 the values of the components in the circuit of FIGURE 2 may, for example, be as follows: transistor 10--type 2Nl42, resistor 17-200 ohms variable, resistor 24-220 ohms, resistor 22-220 ohms, resistor 2939,000 ohms, resistor 2010,000 ohms, capacitor 18-200 microfarads, capacitor 1,000 microfarads, transistor 32type 2N459, transistor 34-type 2N459, transformer 13- conventional silicon iron core having a step-up ratio of about 15 to 1; transformer 27 of a toroidal type utilizing a square hysteresis loop magnetic core; lamp 43-120 volt 6 watt incandescent; source voltage 12 volts.

With the foregoing component values the circuit of FIGURE 3 produced 82 flashes of lamp 43 per minute with four pulses per flash, as shown in FIGURE 3. The oscillation frequency of the circuit including output transistors 32 and 34 Was about 1,100 cycles. Experiments have shown that by using pulsed voltages across lamp 43 instead of continuous voltages, lamp 43 can withstand much higher voltages and short high intensity pulses of light can be obtained. The average power consumed is reduced by utilizing the pulsing system. Thus there has been provided by this invention a circuit which provides high intensity, attention-arresting light impulses from a low voltage source with a minimum of power consumption and a maximum of power source life.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. A transistorized lamp system for producing flashes of light with perceptible flicker in each flash,. including: a self-quenching blocking oscillator producing spaced groups of oscillations at a first frequency; a power oscillator operating at a second frequency coupled to said blocking oscillator and controlled thereby; said second frequency being high with respect to said first frequency; and a lamp coupled to said power oscillator and responsive to the intermittent, modulated energy therefrom to produce flashes of light with visually perceptible flicker.

2. A transistorized lamp system for producing flashes of light with perceptible flicker in each flash, including: a self-quenching blocking oscillator producing spaced groups of oscillations at a first frequency; a power oscillator operating at a second frequency coupled to said blocking oscillator, biased-off in the absence of oscillations from said blocking oscillator and modulated by any oscillations therefrom; said second frequency being high with respect to said first frequency; and a lamp coupled to said power oscillator and responsive to the intermittent, modulated energy therefrom to produce flashes of light with visually perceptible flicker.

3. Apparatus according to claim 2 in which said lamp is an incandescent lamp.

4. Apparatus according to claim 3 in which said power oscillator includes grounded emitter push-pull p-n-p transistors.

5. Apparatus according to claim 4 in which said blocking oscillator includes a repetition rate control.

6. A flashing lamp system producing lamp on periods and lamp off periods, including: an electric lamp; an electric pulse generator having a sub-audible repetition rate and being self-quenching to have on and ofF' periods corresponding to said lamp on and lamp off periods; a lamp power source coupled to said generator and responsive to pulses therefrom to supply power at a higher repetition rate to said lamp for the duration of each pulse, which duration is short with respect to each of said lamp on periods.

7. A flashing lamp system having on periods and off periods, said system including an electric lamp and means for supplying to said lamp during said on periods electrical pulses having a frequency above the visually perceptible range modulated by electrical pulses lying within the visually perceptible range, whereby said lamp is caused to emit a light which flickers perceptibly during its on periods.

8. A transistorized flashing and flickering signal lamp system comprising a signal lamp, a power oscillator having a frequency in the audio range and at least several times the critical frequency for flicker perception in humans, a transformer coupled between said lamp and said power oscillator, a self-quenching blocking oscillator connected to control the keying of said power oscillator between oscillating and non-oscillating states, a timing circuit forming a part of said blocking oscillator and proportioued to establish an on-oif blocking repetition rate for flashing said lamp at a frequency of the order of one cycle per second, and a second timing circuit forming a part of said blocking oscillator and proportioned to establish a flicker frequency component in the output of said blocking oscillator, during each of its on periods, at a rate substantially higher than the blocking repetition frequency but not above the said critical frequency.

References Cited in the file of this patent UNITED STATES PATENTS Stout et al. May 19, 1959 

